This invention generally relates to a multicylinder internal combustion engine of a type generally used in automotive vehicles and, more particularly, to a control device therefor designed to minimize the occurrence of engine knocking.
The control device to which this invention is applicable includes an ignition timing control device, an exhaust gas recirculating (EGR) control device, an air-fuel ratio control device and the like. However, for the purpose of illustration of this invention, the ignition timing control device for the multicylinder automobile engine will be referred to as one example of the numerous control devices to which this invention is applicable.
In general, the ignition timing control device for the multicylinder engine controls the engine cylinders in a predetermined firing order at different ignition timings according to the engine operating condition. It has long been well known that, in the event that a knocking occurs in the engine, the occurrence of the engine knocking can be minimized or substantially eliminated if the ignition timing is retarded a certain angle. Where the ignition timings in all of the engine cylinders are equally controlled as hereinabove described, the ignition timings in those engine cylinders are equally retarded once the knocking has taken place in one of the engine cylinder. This method brings about reduction in engine power output and mileage as the retardation of the respective ignition timings in the remaining engine cylinder is good for nothing, in view of the fact that the engine cylinders have their own characteristics different from one cylinder to another due to, for example, air-fuel charges of different air-fuel mixing ratio and, for a given engine operating condition, some of the engine cylinders will be susceptible to knocking and the others will not.
In order to substantially eliminate the above discussed problem, an ignition timing control device has been provided which is operable to minimize the occurrence of knocking by detecting the occurrence of knocking in one or some of the engine cylinders by the use of a knocking detector and retarding the ignition timing in the or each engine cylinder, in which the knocking has occurred, according to the intensity of knocking. An example of this prior art ignition timing control device designed to minimize the occurrence of the knocking without reduction in engine power output and mileage is disclosed in, for example, Japanese patent publication No. 56-50114 published on Nov. 26, 1981.
According to this publication, an ignition timing control device is disclosed comprising a knocking detector including a sensor and a bandpass filter and operable to detect the occurrence of knocking; a knocking level detector operable upon receipt of an output from the knocking detector to determine the intensity of knocking; a spark advance level determining circuit for selecting the spark advance angle, through which the ignition timing is to be advanced, depending on the intensity of the knocking; a ignition timing determining circuit for controlling the ignition timing according to the spark advance angle determined by the spark advance level determining circuit; and a knocked cylinder detector for counting the number of firing control pulses, which provide the basis for ignition signals with which the respective engine cylinders are fired, subsequent to the detection of one of the ignition signals which is associated with the reference engine cylinder, to identify one or more of the engine cylinders in which the knocking has actually occurred, whereby the ignition timing for each of the engine cylinders can be controlled on a feedback control scheme by detecting the occurrence of knocking in the individual engine cylinders. In other words, the control device according to this publication is so designed that, when knocking has occurred in one or more of the engine cylinders, the respective ignition timings for such one or more engine cylinders can be controlled.
On the other hand, it is generally well known that, once knocking has occurred in, for example, one of the engine cylinders during a particular engine operating condition in which it tends to occur readily, such as a high load, low speed operating condition, not only does the level of such knocking tends to be relatively high, but also the occurrence of the high level knocking in such one of the engine cylinders tends to induce knocking in the other engine cylinders. However, with the prior art control device of the type disclosed in the above mentioned publication, since even though the high level knocking has occurred in, for example, one of the engine cylinders, only the ignition timing for such one of the engine cylinders is controlled despite the predictability of any possible occurrence of knocking also in the other engine cylinders, and the control of each of the other engine cylinders will not be effected unless knocking has actually occurred. Thus, in the event of the actual occurrence of the high level knocking in one of the engine cylinders, the control of the ignition timing for each of the other engine cylinders tends to be belated and, therefore, the possible occurrence of knocking in the other engine cylinders cannot be successfully avoided.